#Docker Service Create How to use the mount option to use a directory on the host

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Mongo DB likes XFS, so the project is to get MOngodb in a docker container to be happy with an XFS volume on the host. Using the mount type bind instead of volume does the trick.

docker service create \
  --mount type=bind,src=<HOST-PATH>,dst=<CONTAINER-PATH> \
  --name myservice \
  <IMAGE>

Give a service access to volumes or bind mounts

For best performance and portability, you should avoid writing important data directly into a container’s writable layer, instead using data volumes or bind mounts. This principle also applies to services.

You can create two types of mounts for services in a swarm, volume mounts or bind mounts. Regardless of which type of mount you use, configure it using the --mount flag when you create a service, or the --mount-add or --mount-rm flag when updating an existing service.. The default is a data volume if you don’t specify a type.

DATA VOLUMES

Data volumes are storage that remain alive after a container for a task has been removed. The preferred method to mount volumes is to leverage an existing volume:

$ docker service create \
  --mount src=<VOLUME-NAME>,dst=<CONTAINER-PATH> \
  --name myservice \
  <IMAGE>

For more information on how to create a volume, see the volume create CLI reference.

The following method creates the volume at deployment time when the scheduler dispatches a task, just before starting the container:

$ docker service create \
  --mount type=volume,src=<VOLUME-NAME>,dst=<CONTAINER-PATH>,volume-driver=<DRIVER>,volume-opt=<KEY0>=<VALUE0>,volume-opt=<KEY1>=<VALUE1>
  --name myservice \
  <IMAGE>

Important: If your volume driver accepts a comma-separated list as an option, you must escape the value from the outer CSV parser. To escape a volume-opt, surround it with double quotes (") and surround the entire mount parameter with single quotes (').

For example, the local driver accepts mount options as a comma-separated list in the o parameter. This example shows the correct way to escape the list.

$ docker service create \
     --mount 'type=volume,src=<VOLUME-NAME>,dst=<CONTAINER-PATH>,volume-driver=local,volume-opt=type=nfs,volume-opt=device=<nfs-server>:<nfs-path>,"volume-opt=o=addr=<nfs-address>,vers=4,soft,timeo=180,bg,tcp,rw"'
    --name myservice \
    <IMAGE>

BIND MOUNTS

Bind mounts are file system paths from the host where the scheduler deploys the container for the task. Docker mounts the path into the container. The file system path must exist before the swarm initializes the container for the task.

The following examples show bind mount syntax:

  • To mount a read-write bind:
    $ docker service create \
      --mount type=bind,src=<HOST-PATH>,dst=<CONTAINER-PATH> \
      --name myservice \
      <IMAGE>
    
  • To mount a read-only bind:
    $ docker service create \
      --mount type=bind,src=<HOST-PATH>,dst=<CONTAINER-PATH>,readonly \
      --name myservice \
      <IMAGE>
    

Important: Bind mounts can be useful but they can also cause problems. In most cases, it is recommended that you architect your application such that mounting paths from the host is unnecessary. The main risks include the following:

  • If you bind mount a host path into your service’s containers, the path must exist on every swarm node. The Docker swarm mode scheduler can schedule containers on any machine that meets resource availability requirements and satisfies all constraints and placement preferences you specify.
  • The Docker swarm mode scheduler may reschedule your running service containers at any time if they become unhealthy or unreachable.
  • Host bind mounts are completely non-portable. When you use bind mounts, there is no guarantee that your application will run the same way in development as it does in production.

Give a service access to volumes or bind mounts

For best performance and portability, you should avoid writing important data directly into a container’s writable layer, instead using data volumes or bind mounts. This principle also applies to services.

You can create two types of mounts for services in a swarm, volume mounts or bind mounts. Regardless of which type of mount you use, configure it using the --mount flag when you create a service, or the --mount-add or --mount-rm flag when updating an existing service.. The default is a data volume if you don’t specify a type.

DATA VOLUMES

Data volumes are storage that remain alive after a container for a task has been removed. The preferred method to mount volumes is to leverage an existing volume:

$ docker service create \
  --mount src=<VOLUME-NAME>,dst=<CONTAINER-PATH> \
  --name myservice \
  <IMAGE>

For more information on how to create a volume, see the volume create CLI reference.

The following method creates the volume at deployment time when the scheduler dispatches a task, just before starting the container:

$ docker service create \
  --mount type=volume,src=<VOLUME-NAME>,dst=<CONTAINER-PATH>,volume-driver=<DRIVER>,volume-opt=<KEY0>=<VALUE0>,volume-opt=<KEY1>=<VALUE1>
  --name myservice \
  <IMAGE>

Important: If your volume driver accepts a comma-separated list as an option, you must escape the value from the outer CSV parser. To escape a volume-opt, surround it with double quotes (") and surround the entire mount parameter with single quotes (').

For example, the local driver accepts mount options as a comma-separated list in the o parameter. This example shows the correct way to escape the list.

$ docker service create \
     --mount 'type=volume,src=<VOLUME-NAME>,dst=<CONTAINER-PATH>,volume-driver=local,volume-opt=type=nfs,volume-opt=device=<nfs-server>:<nfs-path>,"volume-opt=o=addr=<nfs-address>,vers=4,soft,timeo=180,bg,tcp,rw"'
    --name myservice \
    <IMAGE>

BIND MOUNTS

Bind mounts are file system paths from the host where the scheduler deploys the container for the task. Docker mounts the path into the container. The file system path must exist before the swarm initializes the container for the task.

The following examples show bind mount syntax:

  • To mount a read-write bind:
    $ docker service create \
      --mount type=bind,src=<HOST-PATH>,dst=<CONTAINER-PATH> \
      --name myservice \
      <IMAGE>
    
  • To mount a read-only bind:
    $ docker service create \
      --mount type=bind,src=<HOST-PATH>,dst=<CONTAINER-PATH>,readonly \
      --name myservice \
      <IMAGE>
    

Important: Bind mounts can be useful but they can also cause problems. In most cases, it is recommended that you architect your application such that mounting paths from the host is unnecessary. The main risks include the following:

  • If you bind mount a host path into your service’s containers, the path must exist on every swarm node. The Docker swarm mode scheduler can schedule containers on any machine that meets resource availability requirements and satisfies all constraints and placement preferences you specify.
  • The Docker swarm mode scheduler may reschedule your running service containers at any time if they become unhealthy or unreachable.
  • Host bind mounts are completely non-portable. When you use bind mounts, there is no guarantee that your application will run the same way in development as it does in production.

 

Source: Deploy services to a swarm | Docker Documentation

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